How can I move an object using NDOF?
Indeed, presently, there is no ndof_motion field in the python Event struct.

I checked in with Blender's Python API module owner @ideasman42 on the #blendercoders IRC channel, and he gave the thumbs up to expose this data with an added field. So I will try my hand at adding that. Assuming that all works out, it should then be possible to make your proposed addon.